1. Technical Field
The present invention relates to a start-up method for a gasifier applied to an integrated gasification combined cycle facility (IGCC), for example, and relates particularly to a flare system for the gasifier.
2. Description of the Related Art
An integrated gasification combined cycle facility (IGCC) is a power generation facility that aims for higher efficiency and higher environmental cleanliness than conventional coal-fired power generation by gasifying coal and by being combined with combined cycle power generation. This integrated gasification combined cycle facility has the great advantage that coal, which is a resource in great abundance, can be used, and this advantage becomes even greater by increasing the number of coal types that can be used.
A conventional integrated gasification combined cycle facility generally consists of coaling equipment, a coal gasifier, a char recovery unit, a gas purification facility, a gas turbine facility, a steam turbine facility, and a heat recovery steam generator. Therefore, coal (pulverized coal) is supplied to the coal gasifier from the coaling equipment, and a gasifying agent (air, oxygen-enriched air, oxygen, or water vapor) is taken into the coal gasifier.
In the coal gasifier, the coal is combusted to be gasified, thus generating combustible gas (coal gas). Then, the generated combustible gas is purified after an unreacted component (char) of the coal is removed in the char recovery unit, and is then supplied to the gas turbine facility.
The combustible gas supplied to the gas turbine facility is combusted as a fuel in the combustor, thereby generating high-temperature high-pressure combustion gas, and the gas turbine of the gas turbine facility is driven upon receiving a supply of this combustion gas.
In the heat recovery steam generator, heat energy is recovered from exhaust gas that is discharged after driving the gas turbine, thus generating steam. This steam is supplied to the steam turbine facility, and the steam turbine is driven by this steam. Therefore, power can be generated by a generator that uses the gas turbine and the steam turbine as driving sources.
On the other hand, the exhaust gas from which the heat energy has been recovered in the heat recovery steam generator is emitted to the atmosphere via a stack.
In the above-described integrated gasification combined cycle facility, a coal gasifier start-up process includes the following steps (1) to (9).
Specifically, a general coal gasifier start-up process is performed in the following order: (1) nitrogen gas (N2) purging in the gasifier; (2) pressurizing/warming in the gasifier; (3) ignition in the gasifier by supplying air and an auxiliary fuel; (4) supplying gas into the porous filter; (5) ramping (pressurization); (6) supplying the gas into the gas purification facility; (7) switching the gasifier fuel from the auxiliary fuel to coal; (8) switching the gas turbine fuel; and (9) increasing the load.
Note that the above-described process is used for air blown gasification; however, Steps (1) to (7) in the above-described process are used also for a chemical composition plant using oxygen blown gasification.
In such a start-up process, examples of the auxiliary fuel used at the time of ignition in the gasifier in Step (3) include, for example, kerosene, light oil, and natural gas.
Furthermore, in the gas-turbine-fuel switching step (7), a start-up fuel (for example, kerosene or light oil) that is used at the time of start-up during which the supply of coal gas cannot be received is changed to coal gas generated in the gasifier.
Japanese Unexamined Patent Application, Publication No. Sho 62-182443 describes a technology in which, when the integrated gasification combined cycle facility is started-up, a gasifier and a gas purifying device are warmed while combusting exhaust gas in a flare stack (flare facility), until the gas composition and pressure are stabilized, and combustion can be performed in the gas turbine. JP 62-182443 also describes that a smoke emission treatment facility for a flare stack is required at a location with strict environmental conditions.
Furthermore, Japanese Unexamined Patent Application, Publication No. 2006-152081 discloses a coal gasification plant in which a bypass line that branches at an upstream side of a dust removal device and that reaches the flare stack is provided in a main system line connecting the coal gasifier and the dust removal device.